The present invention relates to an integrated circuit package.
Integrated circuits are typically assembled into packages that are mounted to a printed circuit board. A plastic ball grid array (PBGA) package includes an integrated circuit that is mounted to a substrate. The substrate is typically a printed circuit board which has routing traces, power/ground planes and vias that interconnect the integrated circuit to a plurality of solder balls located on a bottom surface of the substrate. The solder balls are reflowed to attach the package to an external printed circuit board such as the motherboard of a computer.
The integrated circuit is electrically connected to the substrate by bond wires. The bond wires are typically attached to the integrated circuit and substrate with a wire bond machine. To prevent movement during the wire bond process the integrated circuit is attached to the substrate with an adhesive. The adhesive is typically a silver filled epoxy which tends to absorb moisture during the assembly process. After the wire bonding process is completed, the integrated circuit, bond wires and substrate are placed in a mold that is injected with an encapsulant which encapsulates the circuit. The solder balls are then attached to the substrate.
The solder balls are typically reflowed by applying heat to the entire package. The heat may convert the moisture absorbed by the epoxy into steam. The creation of steam may crack the package and separate the integrated circuit from the substrate. For this reason the integrated circuit/substrate subassembly is handled in a way to minimize moisture absorption before, during and after the wire bond process. This may require humidity controlled storage and assembly areas. Controlling the humidity during the assembly process increases the complexity and cost of mass producing the package. It would be desirable to provide a PBGA package which is more reliable and less sensitive to moisture in a manufacturing environment.